Electrostatic storage display device



2?, W69 J. M. ENGEL 3,447,021

ELECTROSTATIC STORAGE DISPLAY DEVICE Filed Jan. 13, 1967 10 ERASE 29 CONTROL 4o 36 28 H 21 55 1 T 15 PM", 40

INVENTOR JAN MARCIN ENGEL By kflm ATTORNEY United States Patent 3,447,021 ELECTROSTATIC STORAGE DISPLAY DEVICE Jan Marcin Engel, San Jose, Calif., assignor to International Business Machines Corporation, Armonk, N.Y.,

a corporation of New York Filed Jan. 13, 1967, Ser. No. 609,152

Int. Cl. H01j 31/26 US. Cl. 315- 13 Claims ABSTRACT OF THE DISCLOSURE Cross-references This invention relates to an improvement in the electrostatic writing and printing device described in US. Patent 3,109,062, Clauer et al., issued Oct. 29, 1963.

Background 0] the invention This invention is related in general to electrostatic storage display devices, and relates more particularly to apparatus for developing the image formed in electrostatic display vacuum tubes.

In electrostatic storage display tubes such as that disclosed in the Clauer et al., patent referred to above, an electrostatic image is formed by directing an electron beam towards a dielectric target for storing charges in small discrete areas where the beam strikes. The target surface is held in an evacuated envelope next to a transparent faceplate positioned on the side of the target opposite the electron beam source. In the space between'the target and the transparent window is a supply of small toner particles capable of retaining an electric charge of opposite polarity to that of the charge impressed on the tar-get by the electron beam, and of a suitable color to produce a visible image on the target.

During the writing of the electrostatic charge pattern on the rear surface of the target, the charged toner particles are maintained out of the influence of the electrostatic field of the target surface. Upon completion of the electrostatic writing on the target surface, the toner particles are cascaded across the front side (i.e., the side of the target opposite that side struck by the beam), in some suitable manner such that the toner is drawn towards and .clings to the areas charged by the beam thereby developing the image so that it can be observed through the transparent faceplate. As described in the heretofore referenced patent, the previous method of cascading the toner across the target surface has been by tilting the tube and merely allowing the particles to fall across the surface of the target. This patent describes an improved method for moving the particles across the target surface.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiments of the invention, as illustrated in the accompanying drawings.

Brief description of the drawings In the drawings:

FIGURE 1 illustrates a preferred embodiment of the invention wherein the display tube incorporates a stationary positioned electromagnetic developing mechanism;

FIGURE 2 is a plan view of the faceplate of the display tube illustrated in FIGURE 1 showing the manner in which the developing particles are cascaded across the target surface; and

FIGURE 3 illustrates a second embodiment of the in vention utilizing a mechanically actuated magnetic developing mechanism.

In FIGURE 1 is shown a display device in which can be incorporated one preferred embodiment of the invention wherein a display device 10 includes an envelope 11 shaped like a conventional cathode ray tube. A sealed vacuum cavity 12 is formed within the envelope with a transparent faceplate 14 being included in one end of the envelope and the other end being narrowed down to form a neck 15 in which is held an electron gun 16. Between the faceplate 14 and the gun is positioned a nonconductive target 17 made of a dielectric material. The edges of the target are sealed to the inner wall of the envelope to separate the cavity 12 into two separate vacuum chambers 18 and .19.

The target 17 is held in parallel spaced relationship to the faceplate 14 and serves to provide the writing surface on which images can be formed. To write an image on the target, the electron beam formed by the gun is directed along the neck 15 of the housing to be scanned across the surface 20 of the target by the action of a suitable deflection means such as a deflection yoke 21 disposed around the neck of the envelope. The deflection yoke is energized by a suitable source of sweep voltage signals such as a sweep voltage generator 22. During sweeping, the intensity of the beam is modulated by a video information signal means 24 to write the desired image on the surface of the target. The areas of the target surface 20' struck by the electron beam are changed to a second state by having an electrostatic charge impressed thereon forming a latent image responsive to the video input signals supplied by the signal generator 24. Since the target is made of a dielectric material, this electrostatic charge remains -in the pattern formed by the beam for a period of time.

Within the chamber 19 adjacent the faceplate 14 is placed a supply of small toner particles 25 which are capable of retaining an electrical charge of opposite polarity to that impressed on the target member by the electron beam. These particles are brought into contact with the target after the latent image has been formed thereon by the electron beam and will adhere to the areas on the surface 26 opposite those areas on the surface 20 struck by the beam to develop the image formed. Such particles preferably are of a dark color so as to produce an image of maximum color contrast with the target member 17. The toner particles 25 may be charged in any suitable manner such as by a triboelectric effect produced by mixing them with other types of particles 27 of a dissimilar nature such that agitation of the two particle types produces opposite electrical charges thereon. One example of a suitable material for the toner particles 25 are certain resins or plastics with small glass beads being used as the other type of particles 27.

After the particles 25 have been cascaded across the target surface 26 so as to adhere to the selected areas thereon to develop the image, the image can be viewed through the transparent faceplate 14 of the envelope. While in the embodiment described, the viewing is accomplished .by directly observing the image through the transparent faceplate 14, the image also could be projected for viewing outside the tube envelope by the use of the .proper associated optical devices. Thereafter to remove the image, means such as an electron gun 28 may be utilized to generate a flood beam of electrons directed at the surface of the target. As shown in the drawings, the electron gun 28 extends through the envelope 11 and is operative, when energized by a suitable signal source such as the erase control 29, to produce a large quantity of electrons which are accelerated towards the surface 20 of the target. The flood gun preferably operates by producing a secondary emission ratio greater than unity for all electrons striking the target surface. For every incoming electron from the electron flood beam more than one electron is emitted by secondary emission from the target surface until an equilibrium condition is reached. Thus, the electrostatic charge on the target member 17 is removed. At the same time, the developer again is cascaded over the target suface 26 to remove any remaining particles from it,

In the past, as explained by the referenced patent, the particles have been cascaded across the target for developing the image by tilting the envelope 11. Thus, the particles within the chamber 19 were caused to fall across the face 26 of the target with those coming under the influence of the electrostatic field created by the charge pattern being drawn to and held on the surface 26 of the target after the envelope was tilted back to the normal position shown in FIGURE 1. Naturally, the mounting of the envelope so that it could be tilted and the additional mechanism to effect the tilting greatly complicated the apparatus necessary for the proper functioning of the display device. However, it is very important that any method used for developing the image not affect the operation of the tube such as by exerting an external field which might otherwise influence the path of the electron beam. Additionally, the vacuum environment within the cavity 12 must be maintained at all times for proper operation of the electron beam thereby complicating the use of mechanical connections between the cavity 12 and the exterior of the envelope.

In accordance with the present invention, development of the target image is accomplished with the envelope being mounted in a stationary manner by mixing with the toner particles magnetizable carrier particles such as an iron powder in a specific manner to form the second particles 27 of the triboelectric pairing. By use of an external magnetic field, the magnetizable particles can be lifted up across the target face to carry with them the toner particles for subsequent adherence to the surface 26 to develop the electrostatic image formed thereon by the electron beam. Accordingly, as illustrated in FIG- URE 1, a magnetic means 30 is positioned external to the tube for establishing a magnetic field extending through the chamber 19 for lifting the particles therein up across the face 26 of the target. The magnetizable particles 27 thus are lifted across the target face by the magnetic field of the target means to carry with them the toner particles for developing the image impressed on the target.

In the preferred embodiment, the magnetizable particles 27 are made of an iron powder coated with a polyvinyl chloride chemical. The coating can be accomplished in a manner well known in the art to form the particles 27 comprised of the iron powder completely coated by the polyvinyl material. Thus, the magnetizable particles serve two purposes: the first being to serve as the material for causing the triboelectric effect with the toner particles 25 such that the toner particles will be charged to adhere to the electrostatically charged areas of the target; and the second purpose being to func- 4 tion as a carrier to which the toner particles adhere sufficiently so that as the magnetizable particles are lifted under the influence of the magnetic field, the toner particles are carried therewith to be pulled off by the electrostatic charge impressed on the target 17. Naturally, many other such materials could be used for the purposes just described with the prime requisites being that the particles 27 being magnetizable and the particles 25 being charged at a polarity opposite to that charge impressed on the target by the recording beam.

The magnetic field in the preferred embodiment is produced by the magnetic means 30 which includes a plurality of electromagnets 31, 32, 34, 35, and 36 spaced about the edge of the faceplate 14 and extending from a point at the bottom or six oclock position of the envelope and up one side thereof to the top near the twelve ocl-ock position of the envelope faceplate. Each of these electromagnets includes a coil 37 wrapped around an iron core 38 and connected to the developing control 39 by a conductor 40 with the other end of the coil being connected to ground. The developing control 39 comprises a sequentially actuated switching mechanism such as a stepping switch for supplying energizing current to the conductors 40 in a predetermined sequence. To lift the magnetizable particles 27, the electromagnets are energized in consecutive sequence starting with the coil 31 so as to form a magnetic field moving counter clockwise in the chamber 19 to draw the magnetizable particles up along a path parallel to the target 17, as indicated by the arrows 41, until the uppermost electro magnet 36 is energized. Thereafter, by de-energizing the electromagnet 36 the magnetizable particles are cascaded downward along the surface 26 of the target. The toner particles 25 adhere to the surface of the particles 27 as the magnetizable particles are activated upward to come under the influence of the electrostatic field of the charge pattern formed on the target. Thereafter, the toner particles are pulled away from the magnetizable particles 27 and drawn to and held on the target sur face 26 for developing the image written by the electron beam. This developed image can be viewed through the transparent faceplate 14.

Thereafter, by energization of the flood gun 28, the charge pattern on the target 17 is dissipated to erase the image. At the same time, the electromagnets 31 through 36 again are energized sequentially to cascade the particles 25 and 27 across the surface 26 of the tar get to wipe the surface clean of any toner particles left thereon to prepare the target for the formation of the next image.

A second embodiment of the invention is illustrated in FIGURE 3. The basic envelope, cathode, target and faceplate structure is the same as described in the first em bodiment. Also the particles 25 and 27 are formed in the same manner. However, the magnetic field is formed by a electromagnet 42 which is physically moved up wardly across the faceplate 14 from a position immediately adjacent the particles lying at the bottom of the chamber 19 to a position at the front top edge of the faceplate to lift the particles across the surface 26 of the target. Actuation of the electromagnet is effected by attachment of the electromagnet to a pair of endless belts 44 and 45 wrapped about the pulleys 46 and 47 rotatably held respectively at the top and bottom edges and to one side of the faceplate. The .bottom pulleys 46 are attached to a rotatable shaft 48 leading to an elec* tric motor 49 supplied with electric power through conductors 50 by a developing control 51. Thus, by energi zation of the motor the pulleys 46 are rotated to turn the belts in a counterclockwise direction so as to move the attached electromagnet 42 from a starting position at the bottom of the envelope upward along the faceplate. At the same time, electric current is applied from the developing control 51 to conductors 52 leading to the coil 54 of the electromagnet to establish a magnetic field ex tending into the chamber 19 and serving to pull the mag netizable particles 27 (to which the toner particles 25 are attached) upwards along the target surface, When the electromagnet 42 reaches the uppermost position adjacent the pulleys 47, the coil 42 is deenergized and the particles are permitted to fall or cascade downwards along the target surface. The motor 49 then is reversed to return the now deenergized electromagnet 42 to the starting position. In the same manner as heretofore described with respect to the first embodiment, the toner particles 25 are attracted to the charged areas of the target 17 for developing the image impressed thereon. Thereafter, for erasure, the flood gun 28 is energized to dissipate the electrostatic charge on the target and the particles again can be cascaded across the target for complete erasure of the image previously formed on the target.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

I claim:

1. Apparatus for forming a readable image from an information-bearing signal comprising:

an envelope forming an internal cavity;

a target fixed within said cavity for normal viewing in the vertical plane,

means to change said target from a first to a second state responsive to said signal thereby to form a latent image thereon;

a plurality of particles including magnetizable means in said cavity adapted to adhere to selected areas of said target when in the second state to develop said image, and

magnetic means disposed external to said envelope for cascading said particles and magnetizable means across an inclined surface of said target for developing said image formed thereon.

2. Apparatus as defined in claim 1 wherein said target when in said second state has an electrostatic charge deposited thereon which attracts and holds said patricles for developing said image.

3. Apparatus as defined in claim 2 wherein said magnetizable means includes a material for impressing a charge on said particles triboelectrically.

4. Apparatus for forming a readable image from an electrical information-bearing signal comprising:

an envelope forming an internal evacuated cavity,

a source of particles in said envelope,

a thin walled target fixed within said envelope in a position to divide said cavity into two sealed chambers with a first chamber including said particles source, said target being normally in a first state and being operable when struck by said particles to assume a second state at the immediate area struck,

means to direct said particles to form a beam modulated responsive to said signal for writing an image on said target,

a plurality of toner particles in said second chamber adapted to adhere to the areas of said target in said second state when moved in close proximity to said areas,

a magnetizable material included within said second chamber adapted to transport said toner particles when moved, and

magnetic means positioned outside said second chamber operable to lift said magnetizable material and toner particles upwards across the adjoining surface of said target to develop the image formed thereon.

5. Image forming apparatus as defined in claim 4 wherein said source generates a beam of electrons.

6. Image forming apparatus as defined in claim 5 wherein said target is comprised of a dielectric which assumes an electrical charge at the areas struck by the beam and an electrical charge of opposite polarity is impressed on said toner particles.

7. Image forming apparatus as defined in claim 6 including second particles mixed with said toner particles to charge the toner particles triboelectrically.

8. Image forming apparatus as defined in claim 7 wherein said second particles include the magnetizable material for transporting said toner particles.

9. Image forming apparatus as defined in claim 8 wherein said magnetizable material is iron powder and said second particles are coated with a polyvinyl material.

10. Image forming apparatus as defined in claim 4 wherein said magnetic means comprises an electromagnet selectively energizable for lifting said magnetizable material upwards across the target surface.

11. Image forming apparatus as defined in claim 4 wherein said magnetic means comprises a magnet movable relative to said target for lifting said magnetizable material upwards across the target surface.

12. Image forming apparatus as defined in claim 6 wherein said magnetic means comprises a series of electromagnets spaced around the outside of said envelope near the edges of said target and including electric coils and means for selectively energizing said coils for lifting said second particles across the adjoining surface of said target.

13. Image forming apparatus as defined in claim 6 wherein said magnetic means comprises an electromagnet having an electric coil and being mounted for movement relative to said envelope such that said second particles can be lifted by energizing said coil and moving said electromagnet relative to said envelope.

References Cited UNITED STATES PATENTS 2,979,026 4/ 19 61 Renter 118637 3,032,009 5 /1962 Magnusson 11 8-637 3,109,062 10/ 1963 Clauer et al. 178-6.6 X 3,113,042 12/1963 Hall 118637 RODNEY D. BENNETT, JR., Primary Examiner. JEFFREY P. MORRIS, Assistant Examiner.

US. Cl. X.R. 118-637; 178--6.6; 346-74 

